In laboratories, pipettes are often used in conjunction with pipette fillers. Pipette fillers are commonplace titration aids which comprise a mechanism that is fitted over the end of the pipette and is operated manually to control the dispensing of the titrating fluid.
The pipette filler also protects the health and safety of the operator by removing the necessity for the operator to place their mouth over the non-dispensing end of the pipette is order to suck up the fluid; operators can pass on infections and harmful chemicals may be accidentally sucked into the mouth.
However, these known pipette fillers are relatively expensive. Moreover, they are prone to malfunction caused by leakage through their simple valve mechanisms. When fitted to the pipette, the known pipette fillers make the dispensing equipment top heavy, preventing the equipment being left to stand safely in smaller sized graduated cylinders. Also, the vacuum release principal on which the known pipette fillers work is an indirect control method, which results in poorer control of the dispensing process than is achievable by positive displacement methods.
U.S. Pat. No. 3,848,777 discloses a pipette for receiving and dispensing liquid wherein a plunger in a cylinder is connected to a plunger rod guided in the cylinder and the free end of the rod is U-shaped with a free end having a projection thereon to be engageable in any one of a series of grooves provided at spaced intervals along the outside of the cylinder so as to provide a detent system for dispensing of liquid, the U-shaped portion of the plunger rod having two corrugations to be engaged by the thumb of the user.
U.S. Pat. No. 4,493,704 discloses a portable syringe with a U-shaped thin flexible plunger stem which can be bent over to lie upon the outside of a body of the syringe, the plunger stem having closely spaced teeth thereon engaged by a screw driven by a motor to cause dispensing of liquid.